In this paper, the inverse problem of the medium parameters in an inhomogeneous medium is studied and a generalized ray approximate form of the total wave field is described. First, the acoustic wave equation derived ...In this paper, the inverse problem of the medium parameters in an inhomogeneous medium is studied and a generalized ray approximate form of the total wave field is described. First, the acoustic wave equation derived from the elastic wave equation is studied, the referential variables and perturbational variables are introduced, and the integral equation of the medium perturbational parameters is obtained. Then from the point of view of the local principles of the wave function in an inhomogeneous medium, a generalized ray approximate form of the total wave field in an inhomogeneous medium is described, and attention is focused on the Fredholm integral equation of the first kind. Finally, the medium parameters in half-plane are inversed. Numerical examples show when the perturbations of the medium parameters are about 0.5, this method can effectively inverse its variation. Apparently, this method is better than the conventional Born weak scattering approximation.展开更多
Based on the theory of finite element analysis, an inverse analysis model for the comprehensive medium parameters of the Qinghai-Tibet Plateau is set up. With the help of GPS velocity field, the comprehensive crustal ...Based on the theory of finite element analysis, an inverse analysis model for the comprehensive medium parameters of the Qinghai-Tibet Plateau is set up. With the help of GPS velocity field, the comprehensive crustal medium parameters of the plateau are inversely analyzed and the characteristics of the related movement macroscopically simulated. It is then concluded that the tectonic deformation of the plateau is mainly in the form of a N-S compression accompanied by an E-W stretching, and the present tectonic setting of the plateau should be the result of the collision between the Indian and the Eurasian continents during the Cenozoic.展开更多
This paper first establishes the prior globe dynamical model by geophysics,which is a solid earth elastic deformation model.Then,the parameters of the globe dynamic model can be obtained by inverting the geodetic data...This paper first establishes the prior globe dynamical model by geophysics,which is a solid earth elastic deformation model.Then,the parameters of the globe dynamic model can be obtained by inverting the geodetic data.The inverse method can be used in seismology and geology,and to make earthquake prediction.展开更多
On the basis of previous study of the 1679 Sanhe-Pinggu(M8.0) earthquake,the biggest event in history ever recorded in Beijing and its adjacent area,we made a 3-D strong ground motion simulation utilizing the staggere...On the basis of previous study of the 1679 Sanhe-Pinggu(M8.0) earthquake,the biggest event in history ever recorded in Beijing and its adjacent area,we made a 3-D strong ground motion simulation utilizing the staggered-grid finite differences method to study the distributions of peak ground velocity with different earthquake source models in the Beijing region.In the paper,earthquake source models and a transmission medium velocity model are established and the corresponding parameters are given in accordance to the results from a related previous study.Then,using a three-dimensional finite difference computing program of near-fault strong ground motion developed by Graves,the peak ground velocity caused by a destructive earthquake in the Beijing area is simulated.In our computation model,the earthquake source is 3km in depth,and a total number of 21,679 observation points on the ground surface are figured out.The transmission medium velocity model is composed of four stratums which are the Quaternary deposit,the upper crust,the upper part of the middle crust and the lower part of the middle crust.With the minimum grid spacing of 0.15km,a total of 2.28×106 grids are generated.Using a time step of 0.02 seconds we calculated the peak ground velocity for a duration of 8 seconds.After the analysis of the simulation results,we observed some basic characteristics of near-fault strong ground motion such as the concentration effect of near-fault peak ground velocity,rupture directivity effect,hanging wall effect,and basin effect.The results from our simulation and analysis suggest that the source and transmitting medium parameters in our model are suitable and the finite difference method is applicable to estimate the distribution of strong ground motion in the study region.展开更多
Electromagnetic(EM)metamaterials represent a cutting-edge field that achieves anomalously macroscopic properties through artificial design and arrangement of microstructure arrays to freely manipulate EM fields and wa...Electromagnetic(EM)metamaterials represent a cutting-edge field that achieves anomalously macroscopic properties through artificial design and arrangement of microstructure arrays to freely manipulate EM fields and waves in desired ways.The unit cell of a microstructure array is also called a meta-atom,which can construct effective medium parameters that do not exist in traditional materials or are difficult to realize with traditional technologies.By deep integration with digital information,the meta-atom is evolved to a digital meta-atom,leading to the emergence of information metamaterials.Information metamaterials break the inherent barriers between the EM and digital domains,providing a physical platform for controlling EM waves and modulating digital information simultaneously.The concepts of meta-atoms and metamaterials are also introduced to high-frequency integrated circuit designs to address issues that cannot be solved by traditional methods,since lumped-parameter models become unsustainable at microscopic scales.By incorporating several meta-atoms to form a metachip,precise manipulation of the EM field distribution can be achieved at microscopic scales.In this perspective,we summarize the physical connotations and main classifications of meta-atoms and briefly discuss their future development trends.Through this article,we hope to draw more research attention to explore the potential values of meta-atoms,thereby opening up a broader stage for the in-depth development of metamaterials.展开更多
文摘In this paper, the inverse problem of the medium parameters in an inhomogeneous medium is studied and a generalized ray approximate form of the total wave field is described. First, the acoustic wave equation derived from the elastic wave equation is studied, the referential variables and perturbational variables are introduced, and the integral equation of the medium perturbational parameters is obtained. Then from the point of view of the local principles of the wave function in an inhomogeneous medium, a generalized ray approximate form of the total wave field in an inhomogeneous medium is described, and attention is focused on the Fredholm integral equation of the first kind. Finally, the medium parameters in half-plane are inversed. Numerical examples show when the perturbations of the medium parameters are about 0.5, this method can effectively inverse its variation. Apparently, this method is better than the conventional Born weak scattering approximation.
基金The research results are part of a project carried out in 1999-2002 and financially supported by the US National Foundation(No.ASF EARO125968)in 2001-2003 and financially supported by the National Natural Science Foundation of China(Nos.40271089)the Major Sci-Tech Research Project of the Ministry of Education.
文摘Based on the theory of finite element analysis, an inverse analysis model for the comprehensive medium parameters of the Qinghai-Tibet Plateau is set up. With the help of GPS velocity field, the comprehensive crustal medium parameters of the plateau are inversely analyzed and the characteristics of the related movement macroscopically simulated. It is then concluded that the tectonic deformation of the plateau is mainly in the form of a N-S compression accompanied by an E-W stretching, and the present tectonic setting of the plateau should be the result of the collision between the Indian and the Eurasian continents during the Cenozoic.
文摘This paper first establishes the prior globe dynamical model by geophysics,which is a solid earth elastic deformation model.Then,the parameters of the globe dynamic model can be obtained by inverting the geodetic data.The inverse method can be used in seismology and geology,and to make earthquake prediction.
基金This project was sponsored by the National Development and Reform Commission,PRC(20041138)
文摘On the basis of previous study of the 1679 Sanhe-Pinggu(M8.0) earthquake,the biggest event in history ever recorded in Beijing and its adjacent area,we made a 3-D strong ground motion simulation utilizing the staggered-grid finite differences method to study the distributions of peak ground velocity with different earthquake source models in the Beijing region.In the paper,earthquake source models and a transmission medium velocity model are established and the corresponding parameters are given in accordance to the results from a related previous study.Then,using a three-dimensional finite difference computing program of near-fault strong ground motion developed by Graves,the peak ground velocity caused by a destructive earthquake in the Beijing area is simulated.In our computation model,the earthquake source is 3km in depth,and a total number of 21,679 observation points on the ground surface are figured out.The transmission medium velocity model is composed of four stratums which are the Quaternary deposit,the upper crust,the upper part of the middle crust and the lower part of the middle crust.With the minimum grid spacing of 0.15km,a total of 2.28×106 grids are generated.Using a time step of 0.02 seconds we calculated the peak ground velocity for a duration of 8 seconds.After the analysis of the simulation results,we observed some basic characteristics of near-fault strong ground motion such as the concentration effect of near-fault peak ground velocity,rupture directivity effect,hanging wall effect,and basin effect.The results from our simulation and analysis suggest that the source and transmitting medium parameters in our model are suitable and the finite difference method is applicable to estimate the distribution of strong ground motion in the study region.
基金supported by the Project on Frontier and Interdisciplinary Research Assessment,Academic Divisions of the Chinese Academy of Sciences(Grant No.XK2023XXA001)the National Natural Science Foundation of China(Grant Nos.62422106,62131007,62471109,and 62288101).
文摘Electromagnetic(EM)metamaterials represent a cutting-edge field that achieves anomalously macroscopic properties through artificial design and arrangement of microstructure arrays to freely manipulate EM fields and waves in desired ways.The unit cell of a microstructure array is also called a meta-atom,which can construct effective medium parameters that do not exist in traditional materials or are difficult to realize with traditional technologies.By deep integration with digital information,the meta-atom is evolved to a digital meta-atom,leading to the emergence of information metamaterials.Information metamaterials break the inherent barriers between the EM and digital domains,providing a physical platform for controlling EM waves and modulating digital information simultaneously.The concepts of meta-atoms and metamaterials are also introduced to high-frequency integrated circuit designs to address issues that cannot be solved by traditional methods,since lumped-parameter models become unsustainable at microscopic scales.By incorporating several meta-atoms to form a metachip,precise manipulation of the EM field distribution can be achieved at microscopic scales.In this perspective,we summarize the physical connotations and main classifications of meta-atoms and briefly discuss their future development trends.Through this article,we hope to draw more research attention to explore the potential values of meta-atoms,thereby opening up a broader stage for the in-depth development of metamaterials.
